Remove internal notification caller tokens

docs/implementation.md

@@ -766,3 +766,25 @@ Validation passed: image build, shell/migration tests, live infrastructure check
 `make up` intentionally fails for the still-missing API key. Verified sender must
 also be configured in runtime YAML before rebuilding and starting notifications.
 No backend source changed and no email was sent.
+
+### Task #42: remove internal notification caller authentication
+
+Removed BFF bearer metadata, token configuration/validation, and the notifications
+authentication interceptor. The private gRPC endpoint uses the existing `product`
+storage namespace, preserving notification receipts and idempotency without a
+database migration. NATS authentication and application/user authentication remain.
+
+Removed the caller secret from bootstrap, Vault Agent templates and policies.
+Bootstrap archives and retires both `caller` and
+`services/notifications/callers/bff`; live Vault no longer contains either path.
+Service policies deny both paths. The retirement regression fixture verifies
+repeatability and preservation of the NATS authentication secret.
+
+Validation: `make build`, `make test`, `make lint-backend`,
+`make test-dev-tooling`, `make test-dev-infra`, and `git diff --check`.
+Tests cover credential-free Send/Get, idempotent replay through the real service,
+and absence of outgoing bearer metadata over plaintext and optional TLS.
+`make up` applied the live migration and intentionally stopped at the missing
+Resend API key. No email was sent; full product deployment still awaits the API
+key and configured sender. Delivery continues on `dev-env-42` in
+[PR #43](https://git.sendico.io/tech/sxchnge/pulls/43).